Many new half.com buyers and sellers register only with Half.com, and do not complete their account registration on eBay.
While this may allow you to buy on Half.com, it also causes a bit of confusion.

When you only register on Half.com, your feedback page shows you have zero feedback, and are "Not a Registered User".
For sellers, it may look like you are not a legit buyer, and makes sellers a bit nervous.
For buyers, seeing a seller with "0" feedback deter your item from sellling, as some buyers would rather buy from an experienced seller.

(check out http://reviews.ebay.com/Half-com-Sellers-Protecting-against-Fraud_W0QQugidZ10000000008091498 for more info about fraud)

When you do not register your Half.com account with eBay, Sellers cannot leave you feedback, and you will not be able to leave feedback either.
Feedback (although changed in 2008) still helps show successful transactions between buyers and sellers.  According to eBay:

Only registered members of Half.com (eBay Express) and eBay are eligible to participate in the Feedback process.

If you decide to register on eBay, the nasty "Not a Registered User" tag disappears, and buyers/sellers can leave feedback for you.
On the Half.com discussion board, there have been several posters saying they would gladly leave feedback for a new buyer/seller.

At eBay Live 2008, there was some talk (speculation, nothing guaranteed) that the words "Not a Registered User" may be changed
for people who only register on Half.com, to help with the confusion.  Even if Half.com makes this change, buyers/sellers will still not be able
to get or receive feedback unless they complete their eBay registration.

I hope this helps some people, and am willing to take any suggestions to update or correct any information.

http://shops.half.ebay.com/diskounters

I hope you found this guide useful, and wouldn't mind voting.  Thank you!